Why is the spell checker incorrect on some words?

Words that fail spell check but are correctly spelled: neighbor, institutions judgmental (all in the same message!)

If the spell checker is third party, could you consider a different provider? It’s annoying to apparently fail spell check only to find that the word is spelled correctly.

neighbor is a US variant of neighbour so maybe you should change speelchecker dictionary to U.S. English and the problem solves itself.